Cationized polymeric compounds such as cationized cellulose exhibit hydrophilicity and thickening properties, and are therefore widely used in a variety of fields as thickeners, adhesives, dispersants and emulsion stabilizers and the like.
In these applications, the cationized polymeric compound is typically dissolved in water or a mixed solvent containing water (hereinafter also referred to as an “aqueous solvent”) prior to use, and is therefore usually in a powdered form or fine particulate form to aid dissolution.
However, because these types of cationized polymeric compounds generally exhibit extremely high levels of solubility in water and aqueous solvents, if the compound is simply added to the water or aqueous solvent, then only the surface of each particle is wet by the water and dissolved, and the particles then bond together in clusters, forming undissolved lumps. Once these undissolved lumps form, the contact surface area between the cationized polymeric compound and the water is reduced dramatically, and achieving complete dissolution of the cationized polymeric compound takes considerable time, which can be problematic in an industrial process.
In response to this problem, a glyoxal treatment is known in which a water-soluble polymeric compound such as a cationized cellulose is treated with glyoxal, thereby enhancing the hydrophobicity and improving the dispersibility of the polymeric compound within water (hereinafter referred to as “water dispersibility”) (for example, see Patent Document 1). According to this glyoxal treatment, the glyoxal reacts with the hydroxyl groups of the water-soluble polymeric compound, resulting in cross-linking between the glyoxal and the water-soluble polymeric compound via hemiacetal bonds. This cross-linking hydrolyzes upon treatment with an alkali or heat, and therefore the glyoxal-treated water-soluble polymeric compound disperses with excellent water dispersibility when added to water or an aqueous solvent, and can subsequently be subjected to treatment with an alkali or heat to achieve excellent dissolution.
However, glyoxal has been identified as a mutagenic substance, and therefore an alternative technology to this glyoxal treatment is required.
Silane modification treatment in which a cationized polymeric compound is treated with an aminosilane-based compound has been proposed as an alternative to the glyoxal treatment (see Patent Documents 2 and 3). This treatment improves the water dispersibility by hydrophobization of the particle surface of the cationized polymeric compound. As a result, the formation of undissolved lumps is suppressed, and the water solubility is improved. The processes disclosed in the above patent documents specifically include cationizing a water-soluble polymeric compound under strong alkaline conditions, performing a neutralization, and then reacting the obtained cationized polymeric compound with an aminosilane-based compound in the presence of an organic solvent such as a lower alcohol, thus producing a silane-modified cationized polymeric compound.